A tooth surface coating material comprising a curable composition has heretofore been used for various purposes in the dental field. To prevent decaying or to suppress hypersensitivity, for instance, a tooth surface coating material is applied to a predetermined portion on the tooth surface and is cured to form a cured film. That is, upon coating a predetermined portion on the tooth surface with the cured film of the tooth surface coating material, the decaying can be prevented and, besides, hypersensitivity such as smarting of a tooth can be suppressed. The tooth surface coating material is, further, used as an opaquer for shielding the discoloration of the tooth surface and as a dental manicure for improving aesthetic appearance of the tooth surfaces.
The tooth surface coating material is different from the dental adhesives that adhere and fix a composite resin or a prosthetic material to the tooth with respect to that the tooth surface coating material forms by itself the cured film which serves as the outer surface coating that is exposed directly on the surface of the tooth. The tooth surface coating material, however, shares the requirement of adhesion to the tooth with the dental adhesive. Therefore, though not so many proposals have heretofore been made as tooth surface coating materials, many adhesives have now been proposed having good adhesiveness to the teeth, and it has now been considered that the adhesives can also be applied as coating materials for the tooth surfaces (e.g., patent documents 1 and 2).
Many of the dental curing compositions used as adhesives contain (meth)acrylic acid esters as polymerizable monomers and, therefore, have been blended with photopolymerization initiators without, however, capable of exhibiting a sufficient degree of adhesion to the teeth. Therefore, it has been desired to improve their adhesiveness to the teeth.
In order to effectively improve the adhesiveness of the adhesive to the teeth, it is an accepted practice to pre-treat the tooth in two steps as described below prior to applying the adhesive to the teeth.
(1) Apply an aqueous solution (etching agent) of an acid such as phosphoric acid, citric acid or maleic acid to the surface of the tooth, and etch the hard tooth (mainly enamel).
(2) After the etching, a solution (permeation accelerator or also called primer) containing an amphiphilic monomer such as hydroxyethyl methacrylate (HEMA) or the like and an organic solvent as chief components is applied so that the permeation accelerator permeates into the tooth (dentin).
However, these pre-treatments require complex operations. Therefore, there has been developed an adhesive which is imparted with a function (primer function) equivalent to that of the pre-treatment. For example, a patent document 3 is proposing a dental adhesive containing a polymerizable monomer (acidic group-containing polymerizable monomer) that contains an acidic group such as phosphoric acid group or carboxylic acid group as part of the polymerizable monomer and, further, containing a predetermined amount of water and a photopolymerization initiator. The acidic group-containing polymerizable monomer in this adhesive exhibits tooth deliming property and affinity to dentin. Besides, water contained therein works to effectively conduct the tooth deliming. It is, therefore, allowed to form a cured product that strongly adheres to both the enamel and the dentin in the initial stage of adhesion through a simple operation without the need of conducting the above-mentioned pre-treatment.
The patent document 3, further, proposes blending a polyvalent metal ion-eluting filler (e.g., fluoroaluminosilicate glass) making it possible to further improve the adhesion to the teeth. That is, the dental adhesive has the above-mentioned primer function (deliming function for the teeth and permeation acceleration function for the dentin) and, further, develops ionic crosslinking at the time of curing owing to the interaction among the acidic group-containing polymerizable monomer, water and polyvalent metal ions eluted out from the filler in addition to the radical polymerization of the polymerizable monomer. Owing to the synergistic action of these radical polymerization and ionic crosslinking, there is formed a cured product that strongly adheres to both the enamel and the dentin.    Patent document 1: JP-A-06-256131    Patent document 2: JP-A-10-245525    Patent document 3: JP-A-10-236912